This section provides background information related to the present disclosure which is not necessarily prior art.
Among different types of food, water and other edible contaminations, the bacterial contamination is more commonly observed. The survival and growth of bacteria are always dependent on suitable ambient temperature, atmospheric conditions, moisture and the nutrients provided.
E-Coli is a very commonly observed bacteria in the food items such as peanut butter and spinach, etc., and consumption of E-Coli can lead to different types of health disorders, for example diarrhea.
Detection of E-Coli through usual standard biochemical testing procedures requires longer times (e.g.: 8 to 48 hrs) [Reference 1].
A fast sensor that can reliably detect the E-Coli in food, water and other media would avoid many health hazards in a short notice.
A simple and quick way to sensing E-Coli bacteria is through enzymatic chemiluminescence procedures. For example, the enzyme β-Galactosidase released by E-Coli as a part of its metabolic process can be a very useful biomarker.
The chemiluminescent substrate for β-Galactosidase is phenyl galactose-substituted dioxetane [References 2 and 3].
The Lumi Gal® 530, a commercial formulation of 4-methoxy-4-(3-b-D-galactosidephenyl)spiro[1,2-dioxetane-3,2′-adamantane] can also be a best substitute for the detection and quantification of β-Galactosidase activity [Reference 4].
The chemical reaction between the enzyme β-Galactosidase and dioxetane substrate results in the emission of a light wavelength around 530 nm and thus emitted light could be detected by a photodetector or luminometer to determine the presence of E-Coli. 
Biosensors employing above discussed biomarker and assay have enabled rapid detection of E-Coli [Reference 2].
The efficacy and response time of such biosensors are highly dependent on the surface textures of the sensor; micro/nanostructured surfaces with high reflectance are desired.
In recent years, many studies have been performed on the surface texture of silicon wafer. The purpose is to produce a micro/nanostructure on the surface of silicon wafer, to increase the surface area considerably, and thus enhance the physiochemical process.
However, when the surface of the silicon wafer has a subwavelength structure that is smaller than the wavelength of the emitted light, a strong absorption effect can be produced.
Referring to FIG. 1, the reflectance of the surface is severely diminished with increased pore depth as exemplified in FIG. 2. Therefore, control of the depth, size and separation between these structures is critical for the efficacy of the sensor.
The pores on the silicon surface can be produced in KOH or NaOH etchant. Although such an alkaline etching technique is simple and low cost, it has drawbacks of being time consuming, requires heating and yields poor uniformity. The etching solution must be mechanically agitated for better uniformity of the textured structure on silicon surface. Besides, the presence of alkali metal ions in KOH or NaOH etchant is incompatible with bacteria proliferation, and may be detrimental to the efficacy of the sensor.